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At least 55 records · Page 3Linked to original sources
PubMed1995

[Sources of error in the pre-analytical phase of blood gas analysis].

Analysis of blood gases and blood pH yield important information in many situations of clinical emergencies. We report on a patient in whom pre-analytic errors in blood gas and blood pH measurements resulted in unnecessary further investigations. We therefore studied various pre-analytic sources of error in blood pH and blood gas analysis. Delay in sample processing for more than one hour resulted in an increase of pO2 and pCO2 and a decrease of pH. Excess sodium heparin solution as an anticoagulant (> or = 10% of total volume) led to a significant decrease of pH and pCO2 and to an increase of pO2. Air bubbles (10% of total volume) left in the syringe for 10 min significantly increased pO2. For accurate estimations of pO2, pCO2 and pH, it is necessary to keep the heparin solution below 10% of total volume, to expel all air bubbles from the syringe and to process the blood sample within one hour. Instructions to medical staff on handling blood samples for blood gas analysis should include these possible sources of errors.

Aged↗
PubMed1981

[Regulative resistances during mouth breathing--a source of error determining nasal resistance by pulmonary function tests (author's transl)].

Methods to determine airway resistance - pulmonary function tests - have been recommended for the measurement of nasal resistance. Using the "oscillation method", you can demonstrate in some patients a source of error: Some mouth breathers can have an additional regulative resistance. By means of direct write-out tracings it is demonstrated that the simple subtraction of the resistances (during mouth and nose breathing respectively) is not a reliable method to determine nasal resistance. But the source of error can be recognized using a more luxurious measuring technique.

Airway Resistance↗
PubMed1991

[Sources of error in sonographic diagnosis of the rotator cuff].

Sonography of the shoulder joint has developed into an established examination technique in the diagnosis of periarticular lesions of the shoulder. Sonographic diagnosis of the rotator cuff in particular contains a multitude of possible errors, which are gone into by this study by means of 149 clinically, radiologically and sonographically examined shoulder patients with an average age of 50.5 years. Besides errors made by wrong examination technique such of the transducer as incorrect adjustment of the equipment, insufficient contact of the transducer with the skin and unsuitable choice of the examination plane, there are sources of errors in the interpretation of the sonogram caused by lack of knowledge about physically caused artifacts and sonoanatomical qualities of the shoulder joint. Calcification inside the rotator cuff and the so-called "sonographic inhomogeneity of the rotator cuff" are numbered among the sources of error particular to the shoulder joint. Most errors in sonographic diagnosis of the rotator cuff can be avoided by careful examination of both shoulder joints with an exactly tuned ultrasound device, taking into account the sonoanatomical and ultrasonic qualities. Radiological examination of the affected shoulder joint cannot be replaced by ultrasound.

Diagnostic Errors↗
PubMed1987

Constant force probing with and without a stent in untreated periodontal disease: the clinical reproducibility problem and possible sources of error.

There is presently no satisfactory method of detecting periodontal disease activity at a specified site by means of clinical measurements. This study was designed to examine the possible sources of error with regard to probing measurement reliability. Intra-examiner reproducibility of probing measurements was studied at 766 sites in 10 patients with untreated periodontitis, using a 0.25 N hinged constant force probe (a) with a stent for guidance and landmark, and (b) without stent. The stent made little difference to overall reproducibility of probing depths, though it appeared to reduce variation in different areas. Repeated probing led to an increase in some measurements, perhaps by an effect on tissues. Reproducibility of probing depth was lower in deep pockets, and about 2% of all probing depth scores varied by 3 mm or more at the same site. 4 possible sources of measurement error were noted: visual and tactile observational error, positional error and tissue change. The results are discussed in relation to the clinical detection of periodontal disease activity.

Diagnostic Errors↗
PubMed1978

Potential source of error in official diazepam assays.

A possible source of interference by a benzophenone hydrolysis product with the USP XIX spectrophotometric determination of diazepam in dosages forms is reported. A minor adaptation of the official assay procedures is briefly proposed as one method to correct this error.

Diazepam↗
PubMed1981

Sources of error in Doppler diagnosis of carotid occlusive disease.

Fifty errors with Doppler examination of 356 carotid bifurcations were examined to determine their cause and to establish methods of prevention. Only those errors related to hemodynamically significant stenosis or complete occlusion were considered. The relative frequency of errors in diagnosis of occlusion (30 false-positive or negative versus 31 true-positive) was considerably greater than the rate of inaccuracy for diagnosis of hemodynamically significant stenosis (20 false-positive or-negative versus 89 true-positive). The high error rate in diagnosis of occlusion was attributed to reliance on negative information. The source of error could be established in 48 of the 50 cases. In all but three cases, potential for preventing error existed through use of additional noninvasive techniques such as examination of common carotid resistivity or use of oculoplethysmography. Twenty-two errors of localization of stenosis or occlusion were encountered in addition to the 50 false-positive and -negative errors. In three of these, the errors might have led to patient mismanagement.

Arterial Occlusive Diseases↗
PubMed1987

[Noninvasive measurement of cardiac output using two-dimensional Doppler echocardiography and analysis of sources of error].

The purpose of this study was (1) to analyze the factors responsible for errors in the two-dimensional Doppler echographic measurements of cardiac output (C.O.) and (2) to establish a noninvasive method for measuring C.O. The subjects were 50 cardiac patients who had neither aortic valve disease nor intracardiac shunts. The C.O. was calculated using the following formula: C.O. (l/min) = mean flow velocity (cm/sec) x pi(aortic ring diameter/2)2 (cm2) x 60/10(3) Left ventricular ejection flow velocity was recorded in the center of the aortic ring from the apical approach. Mean velocity was calculated by integration of instantaneous mean velocity in the ejection phase divided by the cardiac cycle length, and was corrected by the Doppler incident angle. The inner diameter of the aortic ring was measured in the parasternal long-axis view at the time of the maximum ejection flow velocity. The following results were obtained: 1. Sources of error in the measurement of cardiac output. 1) Accuracy of instantaneous mean velocity calculating circuit: This calculating circuit was accurate in model experiments using pulsatile flow. 2) Effect of high-pass filter: In model circuits, application of high-pass filter overestimated flow velocity. The higher the cut-off frequency of the high-pass filter, the larger the overestimation. This was probably due to the parabolic flow velocity profile in the circuit. 3) Flow velocity profile in the aortic ring: The flow velocity profile seemed to be flat in the aortic ring except near the anterior aortic wall. Therefore, the effect of the high-pass filter was considered to be negligible in case of clinical application. 4) The effects of shift and size of sample volume: The location of sample volume relative to the aortic valve ring shifted about 7 mm during systole. However, the shift and size of sample volume seemed to have little effect on the measured C.O., because the flow velocity profile was nearly flat in the aortic ring. 5) Ultrasound beam incident angle: From a practical viewpoint, it was necessary to set an incident angle of less than 50 degrees for minimizing the error. We were able to set the angle within 50 degrees in all but one of patients. 6) Diameter of the aortic ring: Two-dimensional echographic measurement of the aortic ring diameter was not so accurate; it seemed to become a major source of error in the calculation of C.O.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1979

Petri dish concavity--a potential source of error in antibiotic assay and agar diffusion antibiotic susceptibility tests.

Concave deformaties of the bottom of Petri dishes are a potential source of error for disk agar diffusion antibiotic assay and susceptibility procedures. This is due to differences in agar depth between the central and peripheral areas of the Petri dishes. We have observed significant concave deformities in both empty and commercially filled 150-mm plastic Petri dishes. For this reason we recommend that inspections for Petri dish deformity be incorporated into microbiology laboratory quality control programs.

Anti-Bacterial Agents↗
PubMed1976

Some sources of error and their effect on Census statistics.

Often the reliability of survey data is examined only in relationship to sampling variances, excluding many other potential sources of error. If the sampling variance dominates the mean-square error, then few mistakes result by considering sampling variance only; however, if sampling variance is only a small part of the mean-square error, serious mistakes in inference could be made. The Bureau of the Census has developed a model describing the joint effect of sampling and nonsampling errors on census statistics. This article shows how a study of the components of error may lead to methods of improving the accuracy and reliability of survey data.

Demography↗
PubMed1984

The inaccuracy of total uterine volume measurements: sources of error and a proposed solution.

Inaccuracies in total intrauterine volumes calculated using the prolate ellipse equation have been reported. No previous study has examined all the sources of error. In this study, a comprehensive approach was undertaken. Measurements were obtained from scans of the pregnant uterus in the prone position using an automated water-path scanner (Octoson) and in the supine position using standard static B-mode scanners. Several conclusions could be drawn: 1) From the Octoson prone scans, uterine volumes obtained using the prolate ellipse formula were markedly different from the true uterine volumes obtained by the summation of stepped areas. This showed that the prolate ellipse formula was inaccurate. 2) From the static supine scans, many observer inconsistencies were found in uterine volumes obtained from the prolate ellipse formula. This made the prolate ellipse formula unreliable. 3) Previously published graphs calculated from the prolate ellipse equation, comparing fetal age with total intrauterine volume, were found to vary accuracy, presumably as a result of 1 and 2. A more accurate approach is proposed. Using the outer uterine wall as the boundary, the stepped area-to-volume values of transverse scans taken at 3-cm intervals were found to closely approximate true volumes, with an average error of only 3.5 per cent. Since these measurements encompass the intrauterine contents and the myometrium, it is suggested that the term "total uterine volume" be used instead of "total intrauterine volume."

Amniotic Fluid↗
PubMed1980

Sources of error in the determination of output voltage of pulse generators by pacemaker system analyzers.

The use of threshold or pacemaker system analyzers with widely different characteristics has introduced potential sources of error in the determination of the output voltage of pulse generators. This is further compounded by the availability of pulse generators with diverse waveform configurations and programmability capabilities. Because of this non-uniformity, the physician must have some rudimentary knowledge of waveform characteristics and appreciate the limitations of threshold or pacemaker system analyzers to avoid the unnecessary replacement of normally-functioning pulse generators.

Electric Power Supplies↗
PubMed1995

Clinical reasoning about new symptoms despite preexisting disease: sources of error and order effects.

BACKGROUND: Previous work that studied the evaluation of new, atypical symptoms in patients with preexisting diseases indicated that physicians largely ignored the past medical history and therefore erred in their diagnoses, when compared to a Bayesian analysis. Other studies have shown that the order in which information is presented to a decision maker can affect the inferences drawn, again contrary to a Bayesian standard. OBJECTIVES: The aim of the study was to investigate the source of disparity between clinical judgment and Bayesian analysis and to investigate the effect of alternative orders of presenting information on diagnostic conclusions. METHODS: Two groups of family physicians received a written clinical scenario. One group was given the past medical history before the history of present illness, the physical exam, and the laboratory data. The second group learned about the past medical history after all other clinical information had been presented. Judgments of test accuracy and probably diagnosis were collected at several points to identify the source of any diagnostic error. RESULTS: For both groups, the major source of error was in estimating the prior probability of disease, not in estimating the accuracy of a diagnostic test or updating opinions following receipt of test results. Although both groups of physicians received the same information, they came to markedly different conclusions about the most likely diagnosis. The group given the past medical history at the beginning of the scenario considered this information much less significant than did the group who received it at the end. CONCLUSIONS: Family physicians deviate from a Bayesian standard of reasoning by wrongly specifying prior probabilities and by being influenced by the order in which clinical information is presented.

Bayes Theorem↗
PubMed1977

Sources of error in measuring cerebrospinal fluid formation by ventriculocisternal perfusion.

Ventriculocisternal perfusion is regarded as a precise method of measuring the rate of formation of cerebrospinal fluid (CSF) but it possesses inherent potential sources of error. Using the technique to measure CSF formation rate in the rhesus monkey, we have observed rate changes when none were expected. Most puzzling has been the steady decline of CSF formation rate at 4 percent each hour during the final five hours of a seven hour perfusion although variables known to affect CSF formation remained stable. In addition, alterations in rate caused by artefacts were observed in experiments in which craniospinal blood volume was changed by sudden changes of either PCO2 or central venous pressure. Mobilisation or sequestration of incompletely equilibrated CSF is believed responsible. In other experiments, a small increase of intracranial pressure produced by increasing outflow resistance was quickly followed by an apparent reduction of CSF formation. We have concluded that to assess accurately the effect a variable has on the rate of CSF formation, one must control perfusion time and craniospinal blood volume as well as intracranial pressure.

Animals↗
PubMed1991

Accuracy of end-tidal carbon dioxide tension analyzers.

Substantial mean differences between arterial carbon dioxide tension (PaCO2) and end-tidal carbon dioxide tension (PETCO2) in anesthesia and intensive care settings have been demonstrated by a number of investigators. We have explored the technical causes of error in the measurement of PETCO2 that could contribute to the observed differences. In a clinical setting, the measurement of PETCO2 is accomplished with one of three types of instruments, infrared analyzers, mass spectrometers, and Raman spectrometers, whose specified accuracies are typically +/- 2, +/- 1.5, and +/- 0.5 mm Hg, respectively. We examined potential errors in PETCO2 measurement with respect to the analyzer, sampling system, environment, and instrument. Various analyzer error sources were measured, including stability, warm-up time, interference from nitrous oxide and oxygen, pressure, noise, and response time. Other error sources, including calibration, resistance in the sample catheter, pressure changes, water vapor, liquid water, and end-tidal detection algorithms, were considered and are discussed. On the basis of our measurements and analysis, we estimate the magnitude of the major potential errors for an uncompensated infrared analyzer as: inaccuracy, 2 mm Hg; resolution, 0.5 mm Hg; noise, 2 mm Hg; instability (12 hours), 3 mm Hg; miscalibration, 1 mm Hg; selectivity (70% nitrous oxide), 6.5 mm Hg; selectivity (100% oxygen), -2.5 mm Hg; atmospheric pressure change, less than 1 mm Hg; airway pressure at 30 cm H2O, 2 mm Hg; positive end-expiratory pressure or continuous positive airway pressure at 20 cm H2O, 1.5 mm Hg; sampling system resistance, less than 1 mm Hg; and water vapor, 2.5 mm Hg. In addition to these errors, other systematic mistakes such as an inaccurate end-tidal detection algorithm, poor calibration technique, or liquid water contamination can lead to gross inaccuracies. In a clinical setting, unless the user is confident that all of the technical error sources have been eliminated and the physiologic factors are known, depending on PETCO2 to determine PaCO2 is not advised.

Algorithms↗
PubMed1995

Sources of error in the spike-triggered averaging method of motor unit number estimation (MUNE).

Motor unit number estimation (MUNE) is an electrophysical technique to estimate the number of motor units innervating a muscle or muscle group. MUNE may be useful as a measure of progression of lower motor neuron loss in amyotrophic lateral sclerosis (ALS). Several methods of MUNE have been developed. The spike-triggered averaging method can be readily performed on EMG machines with signal averaging capabilities and is suitable for estimating the number of motor neurons innervating proximal muscles. We have used MUNE as a measure of disease state in a drug efficacy trial for ALS. From our experience with this method we have identified sources of error which can affect MUNE accuracy. We have investigated these sources and report their effect on MUNE.

Action Potentials↗
PubMed1981

[The risk of gastrostomy in childhood. Sources of error and prevention (author's transl)].

The indication for gastrostomy in childhood arises from the possibilities of decompression and enteral feeding. The demand for an operative procedure to children involves simple technique, safety, efficacy and uncomplicated nursing. The most important sources of error in the creation of a gastrostoma arise from the position and size of the catheter, atraumatic suture technique; on the other hand there is the threat of postoperative extension of the gastrostoma, local infection and sepsis. The results of our own procedure are described and the results given of 172 of our own cases.

Aftercare↗
PubMedDate not supplied

Factors influencing the accuracy of the cardiac output monitoring and diagnostic unit for pneumatic artificial hearts.

The Cardiac Output Monitor and Diagnostic Unit (COMDU) has been the most widely used method to noninvasively determine cardiac output in pneumatic ventricles for the past 10 years. Clinical observation has suggested a discrepancy between the COMDU and expected cardiac outputs. In vivo tests verified and quantified this error. The error sources were examined using in vitro test conditions, with both the inflow and outflow, as well as COMDU flow readings, being analyzed. Transducer and calibration error sources were also identified, and the accuracy of the method for determining cardiac output for the in vitro test conditions was quantified. With a more accurate calibration scheme, the in vitro average error was reduced from -16.2% (range of 0.1% to -41.1%) to 0.1% (range 4.8% to -3.65). The major error sources were identified as missed inflow, transducer calibration and drift, and system variance.

Animals↗